1. Field of the Invention
The present invention relates to an optical apparatus used for a projection type image display apparatus or an image-taking apparatus.
2. Description of the Related Art
A projection lens barrel used for a projection type image display apparatus is constituted so that zooming etc. may be performed by driving each moving lens unit in the direction of an optical axis by arranging a cam ring so as to surround the circumference of a lens barrel body, engaging a cam follower, which is provided in each moving lens unit, with a cam groove section formed in the cam ring, and rotating the cam ring.
FIG. 6 shows an example of a projection type image display apparatus in which such a projection lens barrel is mounted.
Inside an apparatus housing 140, an optical box 150 where an illumination optical system, a color separation system, an image display device, a color synthesis system, etc. are incorporated, a projection lens barrel 120 which is mounted in a light emitting section of this optical box 150, a power supply unit 130, and an electric circuit board 160 which controls an image forming device, forming an original image, an illumination lamp, etc. are contained.
In addition, the structure of the projection lens barrel 120 is shown in FIG. 5. Reference numeral 33 denotes a front fixed barrel and reference numeral 39 denotes a rear fixed barrel. These front and rear fixed barrel 33 and 39 constitute a lens barrel body integrated into a piece. A guide groove (not shown) for guiding a moving lens units, described later, in the direction of the optical axis is formed in the inner circumference of the front fixed barrel 33.
Reference numeral 31 denotes a zoom operation member provided in the outer circumference of the front fixed barrel 33. Reference numeral 32 denotes a cam ring rotatably arranged around the optical axis in the outer circumference of the front fixed barrel 33, and is combined with the zoom operation member 31 with screws (not shown).
Inside the lens barrel body, a plurality of moving lens holding barrels 35, 36, 37, and 38 which supports second to fifth lenses II to V for performing zooming and can move in the direction of the optical axis is contained. In three locations in the circumferential direction of these respective moving lens holding barrels 35 to 38, cam followers 40a (40b, 40c), 41a (41b, 41c), 42a (42b, 42c), and 43a (43b, 43c) are mounted, and each cam follower engages with each of cam groove sections 32a to 32d for each moving lens unit which is formed in the cam ring 32.
Reference numeral 34 denotes a first lens holding barrel holding a first lens I for focusing by moving in the direction of the optical axis, and a male helicoid section 34a is formed in its outer circumference. The first lens holding barrel 34 engages with a focus operation member 30 so as to rotate integrally with the focus operation member 30. Since engaging with a female helicoid section 33a formed in the front inner circumference in the front fixed barrel 33, the male helicoid section 34a can move this first lens holding barrel 34 in the direction of the optical axis by rotating the first lens holding barrel 34 by rotational operation of the focus operation member 30, and can perform the focusing.
However, since the cam ring 32 is arranged so as to surround the outer circumference of the lens barrel body in the lens barrel having the above-described structure, the outer diameter of the lens barrel becomes large in the whole circumferential direction.
In addition, since it is necessary to mount the cam followers, engaged with the cam groove sections 32a to 32d of the cam ring 32, in three locations in the circumferential direction of respective moving lens holding barrels 35 to 38, assembly operation is complicated, and in addition, it also needs much labor to perform adjustment for removing each minute tilt of the lenses II to V, which derives from dispersion in dimensional accuracy as parts every three cam followers, to the optical axis.
Furthermore, in the above-described lens barrel, the cam ring 32 is formed as a metal part from a viewpoint of securing the positional accuracy of the moving lens holding barrels 35 to 38.
However, this cam ring 32 which is a metal part receives noise generated in the power supply unit 130 shown in FIG. 6 to become a factor of generating noise in the electric circuit board 160 near the cam ring 32. This may become a cause of a trouble at the time of driving the apparatus by noise arising in the electric circuit board 160.